LONG BEACH, Calif--Of the different types of economic analyses
used in cost studies of medical therapies, only the cost utility
analysis takes into account quality of life as an outcome, Jane
Weeks, MD, said at the 1995 Quality of Life Symposium, sponsored
by St. Mary Medical Center. To understand how this type of analysis
works, physicians must add two new measurement units to their
vocabulary: "utilities" and "quality-adjusted life
years (QALYs)," she said.
Rather than using dollars or years of life saved as a measurement
unit, cost utility analyses use QALYs, determined by plotting
quality of life versus length of survival, said Dr. Weeks, assistant
professor of medicine, Harvard Medical School, Dana-Farber Cancer
To use quality of life to adjust survival (so that 1 year of life
at a "quality" of X is as desirable to the patient as
6 months of life at a "quality" of 2X), it must be measured
as a "utility," which Dr. Weeks defined as a quantitative
measure of the strength of a person's preference for an outcome.
By convention, "utilities" are measured on a scale of
0 to 1, in which 0 represents death and 1 represents perfect health,
Three major approaches have been used to determine utility scores:
a rating scale, such as a visual analogue scale (see "
Cost Utility Study Shows Value of Aggressive Antiemetic Use"),
completed by the patient in response to questions; the standard
gamble, in which the utility of a health state is assessed
by asking the patient how much he or she would be willing to risk
to improve it; and the time tradeoff, which asks how much
time one would give up to improve quality of life. The point of
indifference occurs when shortened life expectancy with perfect
quality of life is equal to longer life expectancy with lower
quality of life.
Since all three of these methods have problems that make them
difficult to do in a clinical trial situation, Dr. Weeks offered
an alternative method of determining utilities--the "multiattribute
utility approach," or health indices.
In this approach, a standard quality of life questionnaire is
administered and a formula is then used to convert the answers
into a utility score. The formula is determined by surveying a
reference population using standard gamble or time tradeoff techniques.
Several formulas are now available for generating utilities, Dr.
Weeks said. At Dana-Farber, she is involved in developing a cancer-specific
multiattribute scale known as the "Q-tility Index,"
based on Spitzer's Quality of Life Index (QLI), a five-dimension
scale specific for cancer. "For any possible combination
of answers to the QLI, you can generate a utility using the Q-tility
Index," she said.